Permanent thermal label, goes black if ballast temperature exceeds a predetermined limit, mostly used to refuse warranty claims on the grounds of it was incorrectly installed and ran hot before it died.
Interesting, I never heard of those before, both of these lights had cardboard like stuff between the reflector and the ballast, it was very darkened and fell apart when I removed it
Could also be a QC label, added after final visual or electrical testing. Often has a small stamp on it or the initials of the inspector. Colour is often determined by which shift or line did it. I used them as well, to provide traceability to a machine in case of a callback for poor production.
I was refering to if you have people outside it may cause irritable glare. My eyes are very sensitive to light and the glare from my 250w MH walpack bothers me, so that's why I brought this up. If you look at the lume at the angle where the glass of the lume bends, it is glarey.
But 400w of anything is kinda bright for a yard